At present, real-time communication services, for example, voice and multimedia (audio, video, and data), are being provided using specific networking technologies such as public switched telephone networks (PSTN). Typically, voice signals are converted to digital form and then time division multiplexing (TDM) is used to allocate different conversations to periodic time slots. Other popular networking technologies include internet protocol (IP), a formal set of rules for sending data across the internet, frame relay (FR), a telecommunication service providing variable-sized data packets for cost-efficient data transfer, and asynchronous transfer mode (ATM), a high speed networking standard. All networking technologies have their own call control services, for example, integrated services digital network user part (ISUP)-over-TDM and H.323-over-IP/ATM where H.323 is a protocol standard for the real-time transmission of audio, video and data communications. However, providing a single common cost-efficient architecture for real-time communication services for audio, video, and data, that can be offered for any call control protocols, for example, session initiation protocol (SIP), H.323, ISUP, or the like, using any access networking technologies, for example, IP, FR, ATM, TDM, or the like, is a difficult problem.
In addition, a wide variety of networking conditions must be supported. Such networking conditions may include the number of user devices to be connected, the kind of services each user device wants, the types of media each user device likes to use for each call, the frequency of each type of call of each user device, the time of each type of call of each user device, and the peak/average bandwidth required by all media of all calls of all user devices at a given time. In addition, the performance and quality-of-service (QoS) required for each media by each call, whether or not each type of call is made by a fixed or mobile user device, whether or not transcoding needs to be done for audio or video of each call of each user device, and the geographical coverage of all user devices that are connected must also be considered. Other criteria, for example, whether a call is a point-to-point call, a multipoint call, a local call, a long distance call, a national call, an international call, an E-911 emergency call, or the like, are important to be supported. Consequently, a further problem concerns the design of an architecture that is scalable for alternative sets of networking conditions and provides real-time communication services transparently to the end user devices.